The present invention relates to a method and an apparatus for controlling a flow rate of viscous fluid to feed a predetermined quantity of the fluid in a constant flow rate even if the viscosity of the fluid varies due to temperature.
Heretofore, when highly viscous fluid such as a sealing material for bonding (heretofore referred to as "a sealer") is coated on the seam of panels of an automotive body, the sealer is coated by a spraying equipment such as a robot having an automatic spraying gun. In this case, a nozzle of the gun is moved along the seam of the panels and the gun is switched on or off in response to the necessity of the sealing of the panels. In this case, the sealer of viscous fluid is ordinarily fed by a plunger pump driven by compressed air. The pump is coupled with the gun by a high pressure hose and the sealer is fed under a predetermined pressure.
However, this conventional method has a drawbacks as follows. When an atmospheric temperature varies, the viscosity of the sealer varies so that a pressure loss in the hose and the spraying gun varies. Thus, the injecting flow rate of the sealer varies so that the sealer is not unstably injected. Thus, good sealing quantity can not be obtained.
In order to solve the abovementioned drawbacks, a worker operated a pressure regulator in response to the temperature so as to maintain the flow rate of the sealer. On the other way, proposed was an apparatus for obtaining a constant flow rate of sealer by operating a constant-capacity type pump at a constant speed. When the spraying gun is switched on, it take a long time for the injecting amount of the sealer to reach to the predetermined constant flow rate due to the pressure accumulation of the hose. Also, time to reach a predetermined flow rate varies (approx. .+-.20%) due to the temperature. Thus, there arises a drawback that the coating width of the sealer does not become stable (in case of 400 to 500 mm or longer of coating distance) when the gun is moved at a high speed (400 to 500 mm/sec.) to perform the sealing work of the panels in a high efficiency.